The specific objectives of this application are to 1) determine if non-pregnant women who have had a recent spontaneous pregnancy loss between 16 and 23 weeks, or spontaneous labor and delivery between 24 and 29 weeks gestational age, are more likely to have chronic endometrial microbial colonization with U. urealyticum, mycoplasma, aerobic or anaerobic bacteria, or histologic endometrial inflammation during the interpregnancy interval compared to non-pregnant women with recent spontaneous labor and delivery at term; and 2) perform a prospective, randomized placebo-controlled trial of antimicrobial therapy during the interpregnancy interval in women with a previous spontaneous pregnancy loss. In addition to confirming if this therapy eradicates evidence of microbial colonization or inflammation, and prevents recurrent preterm deliveries, multiple secondary analyses will also be performed relating to recurrent preterm birth, to specific organisms, patterns of endometrial histology, and timing of endometrial sampling and treatment.